| 摘要 |
PROBLEM TO BE SOLVED: To provide a digital information transmission system preparing automatic gain control(AGC) optimizing a signal to noise ratio to minimize the distortion of a signal in the system. SOLUTION: This AGC system monitors the distortion of an outer point at the time of arranging the signal points of a complicated modulation format such as a quadrature amplitude modulation(QAM) to adjust AGC of both RF and IF. A receiver consists of at least two steps of AGC gains, namely an RFAGC amplifier is included in a tuner 102 and an IFAGC amplifier 104 is after stage. An IF amplifier is connected with a mixer 106 and a low-pass filter 108 to be driven by a specific frequency to generate a base band signal. The base band signal is digitized by an A/D converter 110 and processed by a gain control circuit 101. The circuit 101 generates the AGC signals of IF and RF controlling the gain of each AGC steps. |
